OK, I usually have brake issues every year that are easy fixes This time I'm scratching my head. Every winter, I always start the car once a week, pull it forward a few feet, run it throught the gears and stay in gear a few minutes, and get the brakes working, using them fairly hard in the 7' or so I can creep the car along. In the last three years, my brake issues have been stuff like replacing springs instead of brake cylinders this way This year, everythign was fine. I took my top end apart to rebuild my lifters, and suddeny; the brakes SUCK. Hard pedal, low braking action. Visually inspected, replaced all four sets of shoes At first, the brakes are great. After two or three stops, the brakes are bad. Hard pedal, low braking action. When they work properly, the pedal is firm and I could hit my head on the windsheild easily. When they work poorly, it feels like extreme brake fade- but the brakes aren't hot
Yes, they are power. Could be leaking. I pulled the hose off the booster the other day and it seemed like it was holding plenty of vacuum though. I'm hoping it's not a seal in the m/c... I'm going to hook a vacuum pump up to a pressure vessel and flush the whole system. Fluid's pretty dirty
Booster check One test ,use a vac guage/pump tool. see if you have 18 " vav from the engime to the booster. Next connect the pump to the booster and see if you can punp the booster up tp 18" vac in several minutes . If the booster wont pump up it is bad, if it does pump up but you can here a hiss sound coming from the booster and the guage reading is droping , it is bad. Also with the engine off pump the peddle to bleed off the stored vac. from the booster if it is holding vac.then push on the peddle , start the engine , the brake peddle should drop slightly when the engine starts. A slight swish sound may be heard under the dash at the rear of the booster after the engine is opperated and the booster vac. is built up. The booster check valve is a factor also ,flow direction to the engine only As you said when you pull the line the booster has stored vac. how much ???
Jeez, I saw 19" Hg when I had a stock cam. I see about 14" now. I'll never get 18" in the booster. When I put this cam in last year, I had zero brake problems I hear no sound from the booster as the engine is turned off I haven't checked vacuum in the booster- I don't have a fitting for that. I can make one
I haven't checked the vacuum in the booster yet, but when I pulled off the hose today, after the car sat for 24 hours, the saound made was "SHHTTTTTTTTOP!sssss I think it's holding vacuum ok because it startled my Dad who doesn't have the best hearing and he was 10' away :laugh:
Were the drums resurfaced when you installed the new shoes? Were the shoes installed with the longest lining on the rear. Glazed drums will act this way. If they were resurfaced but the shop didn't measure the drum for out of spec(typical) you should check the drums for wear. If the drums are too big for the shoes, the shoes won't make full contact and will give a hard pedal with low braking action. An easy way to do this is to remove the drum and inspect the wear pattern on the shoes. The wear pattern will tell the story. You want to see even wear the entire length of both shoes. It's good practice to lay the drum on the bench prior to installation and then lay the shoes inside the drum. Push the shoes to the outside and visually check to see that they contact the drum all the way around.
Drums were turned last year; all are smooth, all are in spec. I check spec, not the shop (I used to do QC for F/A 18 E/F parts I was actually "QC 1" at my shop) I'm using bonded shoes, no more rivets. Brakes were able to be tightened so much I could smell the brakes wearing in (I can tell the difference between this problem and fade due to heat. beleive me, this isn't fade; this was happening before I replaced all shoes, last week. Same problem) All shoes installed correctly. Nothing glazed now, or on the old shoes (I inspected shoes today). No brake fluid in the vacuum hose; inside is dry I made myself a vacuum chamber from PCV pipe and some vacuum fittings with vacuum hose. A one bar vacuum pump drew vacuum on each bleeder through the chamber as the pedal was depressed. I flushed most of the system this way; I drew almost two pints through the system. Chamber held 25" Hg with the bleeders closed and pump off- no air leaks in the brake system or chamber, or else the chamber would have lost vacuum This should have worked. When I was done, I had zero brakes. No resistance, straight to the floor. I don't have the old-timey neoprene front lines anymore, by the way, I'm using steel braided flex line. I had a neo line fail and make a check valve a few years back I re-bled the old-fashioned way. Several times it seemed as if the brake pedal moved nothing, not even air. I used a plastic tube from the bleeder into a reservoir of brake fluid, so as not to pull air into the system back half of the M/C was clear fluid; front half was so dirty I couldn't see the bottom. i could clearly see the demand and compensator in the back half. After I bled the old fashioned way, i hit the brakes, and i heard a 'thup' sound. Still zero brakers I used my vacuum setup to pull fluid out of the m/c, and re-filled with new DOT 3 (same as I had been using) Started the car, pumped the brakes twice, and had something of a brake pedal. Warning light had come on immediately before; now it doesn't come on. Shut off the car and cleaned up. Took about twenty minutes Started the car up, hit the brakes and held them for about a minute. Low, firm pedal, no warning light. The car had sat for twenty minutes, so I didn't have to pump up the brakes Starting to seem like the master cylinder to me now. I have no bleeders in the m/c. Seems as if the primary piston is moving and the secondary piston isn't, since the rear half stayed clear and the front got stayed dirty my feeling is that only the rear half of the m/c is supplying pressure. Chassis manual is wonderfully vague on the whole thing, although I do have a grasp on how the system works. When i hit the brakes, both sides of the m/c will receive fluid, but it seems as if only the back supplies. I guess what I'm saying is I wonder if a seal has ripped in the m/c. Gonna re-bleed a third time tomorrow and see if i can get anything like a safe pedal
The brakes do work a bit now; but I wouldn't drive the car the way the brakes are Re-bled again. The right rear was easy. Nothing but clean fluid as well The left rear- always a large column of air, about 6" long, followed by small bubbles. Each time I would add more fluid to replace what was lost, the same thing happened. makes me suspect the m/c- except why didn the the other side do this if it was the m/c?? Fluid from the left rear is always dirty. Right rear is always clean. So that makes me think the left rear wheel cylinder is bad. I'm going to chase down the wheel cylinder first, just replace it. Luckily the lines are only 5 years old and it should be easy My vacuum chamber worked well- but not to bleed the brakes. SOmething is going on with the brakes in which the pedal must apply pressure to the power piston to overcome a spring, I think, that simply pulling 25" Hg can't duplicate. It was a good idea though
